Forums: Climbing Information: Gear Heads: Re: [petsfed] What determines the rate at which a cam will rip out?: Edit Log

Partner cracklover

Sep 26, 2012, 11:07 AM

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Registered: Nov 14, 2002
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Re: [petsfed] What determines the rate at which a cam will rip out?
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petsfed wrote:
cracklover wrote:
patto wrote:
In theory and in most of the time in practice a cam will either pull at very light loads ie a tug with your hand.

In theory, perhaps, but in practice, this couldn't be more wrong. Tons of placements look anywhere from bomber to scary-as-fuck, and will hold more than a hard tug, but less than full strength.


And this is due almost entirely to the coefficient of friction changing following the destruction of the rock's surface when the cam is loaded.

Patto is not wrong, its just that confirmation bias and a complex reality tend to obscure the theory he's pointing out. The point was that if you look only at the tangent angle and how close the crack is to parallel, but ignore the rock quality of the placement, you'll get a bimodal failure distribution, with peaks at fall-strength and light-tug-with-your-hand. That doesn't mean there isn't a gray area, just that what puts a placement into that gray area has a lot to do with the rock quality. That is, a placement that might fail well above a body-weight load in good, high friction rock might fail at well below body-weight in slick or crumbly rock. If you only compare similarly hard rock, then cams placed in the rock with the higher coefficient of friction will fail less than those in slicker rock in otherwise identical placements.

No, it's just plain silly. You're calling an "exception" nearly every single fall that happens in the real world. I doubt there are many real falls (not counting just slumping onto the piece) that do not cause the cam to either move somewhat, or crack, crush, or dislocate some crystals.

I suspect that the true failure load of cams in the field would be not so much your "bimodal distribution" (with peaks at light tug with your hand and the strength stamped on the cam) but more like a high peak around the rated failure, and then a gradual slope from the strength stamped on the cam down.

There are so many factors that impact the failure strength of the cam, and so many imperfect placements that work "well enough".


(This post was edited by cracklover on Sep 26, 2012, 11:10 AM)

Edit Log:
Post edited by cracklover () on Sep 26, 2012, 11:10 AM

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